ADL GT40 DAC/Headphone Amp & More (Playback 53)

Headphone amps and amp/DACs
Alpha Design Labs (by Furutech) GT40
ADL GT40 DAC/Headphone Amp & More (Playback 53)

I’ve long been a big fan of Swiss Army Knives, and I suppose this goes all the way back to my days as an Eagle Scout who also happened to live in Switzerland. Having a single multi-tasker that can perform the functions of a bag full of individual tools makes you feel like you’re cheating the system, simplifying your life without losing out on functionality.

Audio has seen plenty of multi-taskers over the decades, from the basic stereo receiver to the multi-channel surround soundbar. Most, however, tend to be compromised solutions, doing lots of things, but none of them particularly well. Real high-end systems have traditionally taken the opposite approach, splitting the functions into so many boxes that you need a wall full of racks just to hold them all.

This is why the Alpha Design Labs GT40 by Furutech is so interesting. It takes a 21st century approach to the audio system multi-tasker, combining a lot of the functions that audiophiles want their systems to do today. For many people it can form the centerpiece of a complete system, whether you use headphones, a desktop speaker setup, or a full-blown room filling stereo rig with large speakers.


To understand just what the GT40 can do, it helps to break down its individual functions, as below.


Most obviously, the GT40 is a USB digital to analog converter (DAC). This means that like a high quality external sound card, it can take a digital signal from a computer’s USB port and convert it into an analog signal to feed your system. USB DACs are one of the hottest categories in audio today, and the GT40 is ready to exploit the qualities of your downloaded high-rez audio files. Unlike older DACs, the GT40 doesn’t have an S/PDIF input to handle the output of a regular CD player, but this doesn’t mean you can’t play CDs through your system. All you need to do is play them on your computer, and use its USB output signal to feed the GT40.


Perhaps less obviously, the GT40 is also an analog to digital converter (ADC). This is the feature that really sets the GT40 apart from other similar components. Using the same USB connection to your computer, the GT40 can convert your legacy analog sources into digital files, for storage and future playback on your computer or digital music player. This also means that you can turn anything from LPs and analog tapes to radio broadcasts into files that you can store and playback on your iPod or smartphone, in addition to the computer itself.

MM/MC Phono Preamp

Next, the GT40 is phono preamp. The GT40 may have just one set of analog inputs (via RCA jacks), but it can be changed at the flick of a switch from handling a normal line level signal, to the much weaker output from a phono cartridge without requiring an additional phono preamp. It can even handle both high output moving magnet or low output moving coil cartridges depending on the settings you choose.

Line-Level Preamp

Fourth, the GT40 is a line level preamp. The stereo RCA outputs allow you to connect a power amp or powered speakers directly to the GT40. This signal can come from either the DAC fed by the USB input, or the analog inputs fed by a line level source or turntable.

Headphone Amp

Last but not least, it’s a headphone amplifier. As with the line level outputs, the headphone amp can get its signal from either the digital or analog inputs, letting it play in the other red hot category in audio these days, headphones.

What’s really impressive is how Alpha Design Labs/Furutech managed to incorporate all of these functions, without turning the GT40 into a box festooned with rows of switches and knobs. The front panel has just two buttons, a volume knob, and a headphone socket. Button number one turns the power on and lights up green, while button number two selects between the analog and digital inputs, changing color from blue to red to indicate which one is selected. Around the back there’s a USB jack for the connection to your computer, and one pair of RCA inputs with a switch to change them from line level to a phono input, with separate setting for moving magnet or a moving coil cartridges. A second pair of RCA jacks is for the line level output, and finally there’s a power socket for the included wall-wart power supply.

After reading that long list of functions you might also expect the GT40 to be huge shelf-bending behemoth, but here the GT40 breaks the rules again, packing everything into a palm sized box that weighs just a hair over 1.5 pounds. By using a wall-wart style power supply, the GT40 gets a leg up over many other small USB DACs that rely on the relatively anemic USB bus for their juice. Still, this is one area where I see the potential for further improvements, much like the after-market Monolithic P3 supply boosted the performance of the Perpetual Technologies P-3A DAC a decade ago.

Ease of Use

Setting up the GT40 is about as straightforward as it gets, just connect your inputs and outputs and you’re ready to go. Even the USB input is completely self-installing, and connected without a hitch to my Vista OS ThinkPad laptop. The GT40 could handle just about any type of file I could throw at it, although because it tops out at 96kHz/24-bit, those giant 192kHz files aren’t going to play.

The only application that requires a bit more work involves using the GT40 to make digital audio recording from analog input sources (line-level or phono input, as you chose), where you use the GT40’s USB port as a digital output. In that scenario, you do need to go into your computer’s audio settings to adjust the recording resolution, but that’s about it. I used the GT40 with the familiar (and free) Audacity recording software package, and found them to work well together.


The GT40 can be used in several different capacities, so we need to break down the way it handles each task. They say that a jack-of-all-trades is a master of none, but I found that the GT40 was remarkably competent at just about every task, especially when you consider its reasonable selling price.

Because of the way it works, many of the GT40’s functions are impossible to evaluate in isolation. For example, it’s impossible to hear the DAC other than through either the line stage or the headphone amp. It’s only by using it in several different configurations that you can begin to build a mental impression of how each section performs.

GT40 as a USB DAC

This was perhaps the GT40s most impressive area performance wise. Even though it doesn’t employ the currently popular asynchronous interface to communicate with the computer, the sound of files playing through the GT40 would make anyone understand why computer audio is important for the future of high-end audio.

The sound had a vibrant feeling of life and dynamics, with plenty of sock at the bottom end and fine delineation of upper octave detail. Midrange textures were well fleshed out especially with high-rez files, allowing me to follow individual instruments while keeping everything grooving together as a coherent whole. Qualitative differences between 44.1kHz/16-bit and higher-rez 96kHz/24-bit files were quite audible on those recordings where I had access to both. Overall, I would call this a fine performance for the price, even if the GT40 were just a USB DAC without all of those additional functions.

GT40 as a Headphone Amp

I tried the GT40 with a number of different types of headphones including the HiFiMAN HE-5, Ultimate Ears UE-10 Pro custom IEMs, Sennheiser HD-580 and HD-555, and B&W P5, along with several others. I find that by using a mix of headphones I can get a better read on the sonic character of an amp, balancing out the somewhat brightly tinged qualities of the HE-5 against the smooth laid back perspective of the B&W P5. Based on these observations, the GT40 comes across as essentially neutral through the bass and midrange, with just a little softening at the very top end. Bass quality and detail was superb, although high-powered sustained organ pedal notes showed how the GT40 could eventually compress just slightly as it ran short of steam driving the low-sensitivity HE-5s. With nothing playing into the UE-10s there was a fair amount of hiss if you really opened up the taps, but this volume level would have blown eardrums out if a track had started. There was no hum or other type of noise besides the very low level hiss.

GT40 as a Phono Preamp

As a hard-core turntable user I tend to be especially picky when it comes to phono preamps, so I was delighted to find that the GT40’s phono section was not just some slapped on afterthought. While the stepped up gain of the moving coil input worked fine, it was in the lower gain moving magnet position where I found the GT40 would really sing. Coupled to an Audio Note IQ3 cartridge, this combination slotted into my tweaked out analog-centric system beautifully. Sure my Croft tube preamp is a little more refined and less mechanical sounding, and my Vendetta phono stage is way quieter, but the GT40 had an impressive ability to resolve fine detail and put across vivid midrange textures. Low-priced phonostages are often lacking in dynamic swing, but the GT40 had plenty of smack and power to go with its lovely textured midrange.

I did note that the phono stage is quite prone to picking up noise from surrounding components and power supplies, so some care with placement is needed if you plan to use this feature. Simply trying out different orientations and positions while listening through headphones usually resulted in a quiet spot.

GT40 as a Digital Recording Interface

This is probably the most difficult part of the GT40’s performance to isolate, because you have to play the recorded file back through the GT40 (or another similar device) to hear what you have done. Having said that, when I recorded from LPs it was not too difficult to hear the improvements as you went from a CD-like 44.1kHz sampling frequency to the highest available 96kHz rate. The sound became more liquid and transparent, with a notably improved sense of contrast in the fine high frequency detail. Even at 96kHz the GT40 couldn’t quite fool me into thinking I was listening to the direct analog recording, but it was still perfectly enjoyable and engaging as a listening experience.


I played a lot of music during my time with the GT40, but some highlights are worth noting.

“Song for Bassanio” from the soundtrack to the 2004 movie version of The Merchant of Venice [Decca] pairs a boy’s treble voice against a lute. Playing the ripped CD through the GT40 into my Audio Note amp and Quad ESL57 speakers, it was really quite difficult to differentiate the file playback from spinning the CD directly. The plucked strings of the lute had exactly the same attack and resonance played either way, and treble Ben Crawley’s voice sounded just as crystal pure through the GT40 as from the CD player. Towards the end of the short track a string section enters, and from the CD I felt there was a tad more dimensionality, but even this was a close call.

I played the track “Words of Wonder” from Keith Richards’ Main Offender album [Virgin Records] from the PC over the HiFiMan HE-5s, and found thunderous reggae style bass line could cause the GT40 to run a little short on power if you really cranked it up. While the amp didn’t audibly clip, there was a slightly compressed quality that would take some of the pop out of drummer Steve Jordan’s wickedly powerful rim shots. When I switched over to the much easier to drive UE-10s this slight dampening of the transient speed disappeared, and sound regained its familiar jump factor.

I transferred the track “Goodbye Pork Pie Hat” from Charles Mingus’ album Mingus Ah Um on SACD [Sony], using the analog outputs of my Oppo universal player into the GT40’s analog line input. I transferred it three times, using the 96kHz, 44.1kHz, and 32kHz settings (skipping 48kHz), and compared the results. The 96kHz version was really very close to the SACD, with just a little of that “direct from tape” solidity and smoothness missing. However, with the 44.1kHz version the differences became clearer, with the spit in Booker Ervin’s sax harder to separate out from the overall tone of the instrument, and a diminished sense of space around the individual players. I should note, however, that these differences really have more to do with the DSD vs. PCM debate, than any performance issues with the GT40.


Consider this product if:

You want to build a computer audio-based system, but also have legacy analog sources that you want to listen to or archive digitally. While it does work great in the context of a full-sized home audio system, the GT40 really comes into its own for the headphone or desktop audio listener.

Look further if:

You have digital gear with only an S/PDIF (coax or optical) interface that you want to incorporate into your system. ADL has an upcoming product called the Esprit, which adds this feature, but also loses the GT40’s phono stage. You should also keep looking if you have very low impedance or ultra low sensitivity headphones that you treasure. Some other amps have more ultimate driving power than the GT40.


•Tonal Balance: 8
•Clarity: 9
•Dynamics: 9
•Output Flexibility: 10
•Value: 10


The GT40 shows us that a jack-of-all-trades really can be the master of all. While it might not get hard-core audiophiles drooling to use it in the most extreme megabuck systems, I’d be hard pressed to name any product that can clearly outshine the GT40 in just one of its many functions for the same money. When you add all of those functions together, the result is clearly a bargain.


Alpha Design Labs/Furutech GT40 USB DAC/ADC, phono stage, headphone amp, line preamp
Accessories: Power supply and USB cable
Frequency response: 20Hz - 20kHz, (+0.5db @ 40Hz, -0.5db @ 15kHz)
THD + Noise: S/N ratio -90db (A-weighted, line output)
Analog Inputs: Phono cartridge (MC/MM); line level on RCAs
Digital Inputs: USB 2.0, type B connector
Analog Outputs: Line level (single ended RCA); ¼ inch headphone jack
USB DAC: Up to 96kHz/24-bit
Digital Outputs: USB 2.0 up to 96kHz/24-bit
Input Impedance: 47k Ohms (MC/MM phonon), line (no spec)
Headphone output impedance: Headphones with 16-300 Ohms impedance recommended
Headphone power output: 80mW @ 32 Ohms
Power supply: 9 Volt wall wart-type
Dimensions (H x W x D): 2.25” x 5.94” x 4.17”
Weight: 28 ounces
Warranty: 1 year, parts and labor
Price: $525.00

Manufacturer Information

Furutech - Alpha Design Labs

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